The disclosure relates to an extraction process for improving propylene yield.
Fluid catalytic cracking (FCC) is a catalytic hydrocarbon conversion process accomplished by contacting heavier hydrocarbons in a fluidized reaction zone with a catalytic particulate material. The reaction in catalytic cracking, as opposed to hydrocracking, is carried out in the absence of substantial added hydrogen or the consumption of hydrogen. Various products may be produced from such a process, including a naphtha product and/or a light product such as propylene and/or ethylene.
There have been several development efforts to increase the propylene yield from an FCC unit. One of the solutions has been to recycle the 4- and/or 5-carbon olefin product back to the FCC unit in order to selectively crack these components to propylene. Another solution is to recycle the olefins back to a second reactor optimized to convert the olefins to propylene. In this case, a separate recovery section is needed to process the product from the second reactor. This configuration works well at low to moderate propylene yields, but if higher yields are required, then the amount of material that needs to be recycled increases rapidly as the 4- and/or 5-carbon paraffins are not separated from the 4- and/or 5-carbon olefins in most FCC processes. As the paraffins cannot be rejected, this inert material must also be recycled in order to be able to recycle a greater amount of the olefin material.
Therefore, what is needed is a new process configuration which allows for the advantages of a traditional FCC unit configuration, but improves the overall configuration by allowing for the 4- and/or 5-carbon paraffins to be separated from the 4- and/or 5-carbon olefins. The overall FCC process recovery section is simplified compared to a process using the aforementioned second reactor as a common recovery section can be used.